This invention relates to fuel cell powering systems, especially with regard to meeting the dynamic requirements of fuel and air supply subsystems.
Fuel cell powering systems have the potential to become an economically viable means of converting chemical energy to electrical energy. For example, in a polymer-electrolyte membrane (PEM) fuel cell, also known as a proton exchange membrane fuel cell, hydrogen and oxygen are the elements to be combined in the production of electrical energy. Air is the customary source of oxygen while the oxidant can be hydrogen or a source of hydrogen such as methane, natural gas or other hydrocarbons. The fuel source may require a local refining process to produce hydrogen and the refining apparatus will include or be called a reformer. The energy conversion in the fuel cell occurs through a process of oxidation, which relies upon the pressurization of both the oxidant, and the oxidizing agent.
Electrical powering systems utilizing fuel cells are comprised of several subsystems requiring the compression of air and/or other gases in order to operate. Each of these subsystems operates best under distinctly different pressure profiles. As a result, the common approach is to utilize a complete gaseous supply system, including a compressor, a drive motor, a motor controller and perhaps an expander for each subsystem in order to meet the unique pressure requirements of each. Such a solution, however, is a significant source of cost, size and inefficiency since it creates a large size power unit with each gaseous supply subsystem operating as a parasitic user of developed electrical energy. If each subsystem is separate, each contributes to the component costs for the fuel cell powering system including auxiliary drive motors and speed controllers for each subsystem. In recognition of these fixed cost drivers, the primary means in which this invention purports to obtain system cost reduction and simplification is through the integrating of both the fuel delivery pump/compressor (gas or liquid) and the air delivery pump/compressor onto the same powered drive train. The immediate cost benefit to integrating the fuel and air pumps onto a common drive is the elimination of multiple electric drive motors and associated motor speed controllers.
To avoid the need for multiple air and fuel supply apparatus, it is preferable, from the perspective of reducing the system complexity, for all compressed air and gaseous fuel consuming subsystems to operate at the same common pressure. A common system pressure requirement enables all of the subsystem gaseous supply needs to be met with a single, appropriately sized compressor. However, while it may be possible for some powering systems to force the various subsystems to operate at a common pressure, such an operating strategy usually entails a large sacrifice in the performance of some or all of the fuel cell subsystems. The result is a solution that saves space but does so at the cost of system efficiency. Additionally, such a solution may also result in an unacceptable loss of flexibility for many applications and is therefore inappropriate in those cases.
Briefly stated, this invention provides for driving both the fuel (oxidant) compressor and the air (oxidizing agent) compressor from the same motor driveshaft and if expanders are included in system design, returning energy from the fuel supply subsystem and/or the air supply subsystem to the motor driveshaft either directly or indirectly.
While system cost is greatly reduced by driving both the fuel and air compressors with a single drive motor, flexibility must be preserved in providing the separate mass flow and pressure requirements of each subsystem. Various embodiments are described herein for meeting flexibility requirements including differential transmissions, variable speed transmissions, throttle and bleed valves, compressors and expanders with multiple, independent inlets and outlets, utilization of variable flow control techniques including flow directional control and combinations of these approaches, together with speed control of the drive motor with feedback signals incorporated into a servo system. Finally, the inventive methods and system incorporate water management techniques further improving system efficiency.